I know that light (such as that emitted by a fluorescent bulb) is generated by electrons falling into lower energy states and releasing an amount of energy as a photon. But radio is transmitted by producing an alternating current in a conductor, and (I assume) it's the acceleration and deceleration of this electric charge which creates the changing electromagnetic field which propagates away from the source. Can light be produced in the same way? Is it feasible to produce an alternating current in the order of 600THz? If so, could we produce things like sawtooth, triangle and square light rather than the usual sinusoidal? I have a feeling there's some 'springyness' to electron interaction and it would be difficult to produce a frequency of 600THz in any conductor larger than about 500nm, but I'd like to hear some thoughts on it. Similarly, do any atoms contain such close-together energy levels that an electron might produce something in the order of kHz or MHz when it falls to a lower energy level, or do all radio waves have to come from some kind of alternating current?